target-arm: Add support for 'Standard FPSCR Value' as used by Neon

target-arm: Add support for 'Standard FPSCR Value' as used by Neon

Add support to the ARM helper routines for a second fp_status value
which should be used for operations which the ARM ARM indicates use
"ARM standard floating-point arithmetic" rather than being controlled
by the rounding/flush/NaN settings in the FPSCR.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Aurelien Jarno <aurelien@aurel32.net>
Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>